Coating apparatus

ABSTRACT

A generally closed housing includes means to pass a continuous length material therethrough. Means define a path within said housing for immersing said material in a tank of coating stuff and thereafter pass through a solvent-vapor atmosphere provided by a boiling tank disposed within the housing. Cooling means determine generally the extent of the gaseous environment and means are provided to recover solvent therefrom.

United States Patent [72] Inventor Kenneth S. Surprenant [56 R fer n Cited UNITED STATES PATENTS [21] Appl. No, 862,569

. 2,024,248 12/1935 Rafton 118/423 UX [22] 2138 57s 11 1938 11 hb 11s 48 ux Division ofSer. -11.5055z0.o61.2s.1965, abandonett 2,274,726 3/1942 Melton 118/67 2,332,309 10/1943 Drummond 118/48 Paemed 1971 3 015 576 1/1962 Hendrixson 6161 118/61 ux [73] Assignee The Dow Chemical Company Midland, Mich 3,042,547 7/1062 P1ckett 117/102 Primary ExaminerMorris Kaplan At!0rneysGriswold and Burdick, C. E. Rehberg and G. R.

Baker [54] ABSTRACT: A generally closed housing includes means to g pass a continuous length material therethrough. Means define [52] U.S.Cl 118/61, a path within said housing for immersing said material in a 118/48, 118/423, 118/642 tank of coating stuff and thereafter pass through a solvent- [51] Int. Cl 1305c ll/00 vapor atmosphere provided by a boiling tank disposed within [50] Field of Search 1 18/58, 61, the housing. Cooling means determine generally the extent of 642, 65, 67, 68, 405, 419, 420, 423, 429, 425; 117/107 L; 156/345; 134/64; 58/5-4 D, 18-2 C the gaseous environment and means are provided to recover solvent therefrom.

PATENTEU JUL27 Ian 3; 5 95 205 sum 2 0F 2 INVENTOR- Ke nnef/z i sur o/"en an 7 BYE HTTORNEY COATING APPARATUS This application is a division of application Ser. No. 505,520, filed Oct. 28, 1965 and now abandoned. The present invention relates to a new and useful apparatus for treating a fabric, sheet, web or film of natural or synthetic material with a finishing agent or an impregnating agent.

The finishing and impregnation of fabrics, paper and the like to impart a property such as water repellancy, wet strength, stain repellancy, smooth surface, crease resistance and the like is a very old art. As the demand for treating such materials increases, the industry seeks an improved technique to apply the chemicals which impart these properties. Older techniques require the use of flammable solvents, long drying and curing periods dictated by the inability to remove the solvents from the base materials many of which are heat sensitive. These prior art techniques are costly because of the large solvent losses, the great quantity of air which must be cleaned of the solvent vapors before being released to the atmosphere or reused.

It is therefore a purpose of the present invention to provide a apparatus for the rapid and efiicient application of treating agents such as finishing and impregnating agents onto and into fabrics, sheets, webs and film.

It is another object of the present invention to provide a apparatus for the rapid drying of fabrics, sheets, films or webs so treated.

Another object of the present invention is to provide a apparatus in which the solvent losses of solvents for the finishing and/or impregnating agents are minimized.

A still further object of the present invention is to provide a apparatus which is capable of accomplishing the aforesaid objects as well as curing, setting, flowing or otherwise fixing the finishing and/or impregnating agents onto and into said fabrics, sheets, webs or films.

These and other objects will become apparent from the following description with particular. reference to the drawings and appended claims. In the drawings:

FIG. 1 represents a vertical diagrammatic section through one form of apparatus which may be used to carry out the process of the present invention; and

FIG. 2 is a diagrammatic vertical section of a modified form of apparatus which may be used to carry out the process of the present invention; and

FIG. 3 is a vertical diagrammatic section of still another modification which may be used to carry out the process of the present invention in which the web of set material isdried with the idea of infrared heat.

In accordance with the present invention a web, sheet, film or fabric, such as one prepared by weaving, casting, screening or the like natural or synthetic fibers, threads or yarns, is introduced into a zone wherein a treating agent as for example a finishing or impregnating agent, dissolved or suspended in a volatile organic solvent is sprayed, doctored, flooded or otherwise applied to one or both sides of the material to be treated. The so treated material is then introduced into a zone of vapors of the volatile organic solvent and passed over heat surfaces or underneath infrared heat sources. After being subjected to both heat and the vapors of the solvent the material passes into a zone of substantially solvent free air wherein additional heating of the material can be carried out. The material upon being removed from the latter zone is substantially free of solvent and retains the treating agent or finishing or impregnating agent evenly distributed on or through the materia].

The volatile organic solvent which can be employed to dissolve or suspend the treating, finishing or impregnating agent is one which has a molecular weight of at least twice the molecular weight of air. Solvents which thus can be employed are the chlorinated hydrocarbon solvent, the fluorinatcd hydrocarbon solvents, the aliphatic and aromatic solvents, petroleum solvents and the like. Particularly useful and preferred are the chlorinated hydrocarbon solvents,

methylene chloride, trichloroethylene, perchloroethylene and methylchloroform. Similarly, the preferred and particularly useful fluorinated hydrocarbons are the polyfluoro; mixed polyfluoro bromo; mixed polyfluorochloro methanes and ethanes, commonly referred to by the codes F11, F112, F114B2, etc. The more desirable hydrocarbon solvents are benzene, toluene and hexane. Although many other solvents fall within the definition set forth they are not known to have as general a utility and low cost of those specifically set forth. However, in certain applications of the present process to special fabrics, or plastic materials other solvents may be used to avoid damage to the base material being treated.

The scope of the treating agents, finishing agents and/or impregnating agents is very broad. For example, fluorine or silicone containing moisture and stain repellants can be applied by using the techniques of the present invention. Likewise, paper finishes, crease resistant agents, for both fabric and paper, wet strength agents, surface filler, surface coatings and the like. In so far as is presently known the only criterion of the agent is that it be one which can be dissolved or suspended in volatile organic solvent of the class aforementioned. Thus, one can, according to the present invention, even apply an agent which will undergo a chemical change upon heating.

Apparatus which can be employed in carrying out the present invention are shown in diagrammatic cross section in the drawing. The following description of the apparatus has particular reference to the apparatus shown in FIG. 1. The apparatus consists of a housing 10 having an inlet 11 and an outlet 12. Integral with the housing walls extending around the entire periphery below the inlet 11 and outlet 12 is a cooling means or cold wall 13. This cooling means prevents the housing walls above it from heating up. Inside the housing 10 in juxtaposition to the'cooling means 13 are several cooling coils 14 through which a cooling medium, such as cold water, can be passed. Directly beneath the cooling coils 14 is positioned a trough 15 into which solvent which condenses on the cooling coils M can be collected. A heating coil 16 in this embodiment shown as a steam heater, is positioned to provide when covered the solvent a boiling sump 17. A number of guide rolls l8, 19, 20, 21, 22, 23, 24, and 25 are situated throughout the interior of the housing 10 above the boiling sump l7, and below the cooling soils 14. One or more of these rolls may be heated by steam, electric heaters or direct fired heaters. In the present embodiment the large guide rolls 19, 21, 22, 24, and 25 are illustrated as steam heated rolls. A second set of guide rolls 26 and 27 are positioned in the zone above the cooling coils 14. These rolls 26 and 27 are illustrated as merely guide rolls, however, either or both may be heated in the same manner as described for the rolls in the lower section of the housing.

It is to be understood that the embodiment of apparatus shown in FIG. 1 does not include the chamber or zone for applying the treating agent. In this particular embodiment of apparatus the treating agent dissolved or suspended in the solvent is applied by a doctoring, spraying or flooding technique known and used in the industry. The application is to be conducted immediately prior to introduction of the base material into the apparatus illustrated in FIG. 1.

The apparatus illustrated in FIG. 2 of the drawings is a modified version of apparatus shown in FIG. 1 which modifications include a sump for holding the treating agent when dissolved in the volatile organic solvent thus permitting application of agent and drying within a single housing. The following description of the apparatus has particular reference to FIG. 2. A housing 30 is provided with an inlet 31 and an outlet 32. The housing 30 has an offset 33 at one side being offset below the inlet 31 and the outlet 32. The offset 33 contains a cooling coil 34 and a boiling sump 35. The boiling sump 35 is provided with heating coils 36 which are illustrated as steam rolls. Guide rolls 37, 38 and 39 are provided at the inlet 31 and near the bottom of the housing 10 the latter two rolls 38 and 39 being below the sump 35 wall 35a and positioned to immerse a material passing around them beneath a solution or suspension of treating agent and solvent. Above these guide rolls 38 and 39 and below the horizontal plane passing through the cooling coil 34 are a series of guide rolls 40, 41, 42, 43, 44 and 45 which are shown to be steam heated, although other sources of heat energy may be employed to heat these rolls. Above the latter series of rolls are two rolls 46 and 47 which are also illustrated as steam heated in this embodiment of apparatus. These rolls perform final drying or curing or heat flowing if necessary.

It is to be understood that the two apparatus illustrated in FIGS. 1 and 2 and described above as well as the modification shown in FIG. 3 and described hereinafter each have associated with the guide rolls, both heated and unheated, a source of motive power, not shown, capable of turning or rotating these guide rolls to facilitate the passage of the base material being treated through the various sections of the particular apparatus.

The apparatus shown in FIG. 3 comprises a housing 50 having an inlet 51 and an outlet 52. The housing 50 is provided with a cold wall 53 integral with the side walls at housing 50. The housing is also provided with cooling coils 54 extending about the inner periphery juxtapositioned with respect to the cold wall 53 and a collecting trough 55 beneath the cooling coils. A sump 50 a is provided in the bottom portion of the housing 50. The sump has a pair of heating coils 50b for providing heat to boil the solvent in sump 50a. A series of guide rolls 56, 57 and 58 is positioned within the interior to guide a web or sheet from the inlet 51 downwardly into the lower portion of the housing 50 and upwardly to a second set of guide rolls 59 and 60 located in the upper portion at the housing 50. Positioned in the upper portion at the housing 50 so as to direct their heat onto a web passing through the lower portion of the housing 50 and around rolls 57 and 58 are a series of infrared heat sources, illustrated as infrared heat lamps 61 and 62. Also positioned in the upper portion of the housing 50 but above roll 60 is a second series of infrared heat sources, also illustrated as infrared heat lamps 63 and 64. Located in the top of the housing 50 is a conduit 65 which connects the interior of the housing 50 to a refrigeration unit 66 through conduit 65:: to a heating unit 67 provided with a fan 68, then by conduit 65b to the outlet 52.-This latter series of elements draws air from the upper portion of the housing which air may contain a small amount of solvent vapors, and refrigerates the solvent-air mixture thereby to condense the solvent and free the air of solvent. The solvent free air is drawn into heater 67 by fan 68, and heated to the temperature of the solvent-air mixture in the upper portion of the housing 50. The so heated solvent-free air is then reintroduced into the housing through outlet 52 passing across the the treated dry material. This current of air forces the solvent-air mixture away from the outlet 52 and wipes the treated dry material free of any solvent-air mixture carried along to the opening, thus minimizing loss of solvent from the upper portion of the housing.

The process of the present invention is hereinafter described in a general manner. The treating agent is applied to the materials by spraying the material. The agent is applied to one or both sides of the web, sheet, fabric or film. The so treated material, which is burdened also with solvent, is passed into a zone maintained substantially full of the volatile solvent vapors of the solvent employed to dissolve or disperse the agent. During the passage through this vapor zone, the web, sheet or film passes over heated surfaces or under infrared heat sources wherein the solvent is removed by evaporation from the material. The material is then passed into a substantially quiescent zone where little or not solvent vapors are present, but wherein heating of the web, sheet or film can be continued to cure or otherwise react, set or fiow the treating agent. The level of the vapor zone is maintained by cooling coils and cold walls. The web, sheet, fabric or film is preferably passed into the vapor zone over a heated surface such as a roll or rolls to drive-ofi" solvent from the web and simultaneously supply heat to fiow, set and/or cure the treating agent if necessary. As a result of these operations there is little loss of solvent.

The following recitation describes the method of the present invention with particular reference to the drawings: a sheet, web, film or similar configuration of plastic film or a fibrous woven or paperlike material is fed to a treating chamber which is but a confined space in which the treating agent and the volatile solvent carrier are applied to the material. The space is preferably adjacent to the apparatus for carrying out the present invention or it may be an integral part of the apparatus as clearly shown in FIG. 2. The following description has particular reference to the apparatus illustrated in FIG. 2. A web 48, for example, enters chamber 30 through an inlet 31 passing onto a guide roller 37 and thence downwardly into a treating zone 49 which contains a solution or dispersion of the treating agent in a volatile solvent such as for example trichloroethylene. The web 48 picks up solvent and treating agent during its passage through zone 49. It is to be understood that the concentration of the treating agent is maintained in the treating zone 49 by well known techniques and is not a part of the present invention. The web 48 is directed into, through and out of the vapor zone 49 by roller 39. The web 48 then progresses to an intermediate zone 49a which is a zone of substantially pure vapors of the organic solvent used in the treating zone. The solvent vapors in the intermediate zone 49a are maintained by boiling solvent in a sump 35 heated with for example, low-pressure steam, electric or gas fired direct immersion heating coils 36.

The web material 48 upon entering the vapor zone 49a passes over a series of heated rollers 41, 42, 43, 44 and 45 then into an upper zone 49!; substantially free of vapors of the solvent. The exact number of heated rollers in any section is not critical but sufficient should be present to bring the web 48 and the surrounding vapor atmosphere to a temperature above the boiling point of the solvent and to such higher temperature as necessary to flow, cure, set or fix the treating agent when such is necessary while simultaneously driving the solvent from the fabric. The web 48 passes from the heated rollers in the intermediate zone 49a into and through the upper zone 4% over heated rollers 46 and 47 to effect additional drying of the fabric and setting or curing of the treating agent may take place. The web 48 is dry, free of solvent and the treating agent flowed, set, fixed or if of a curable nature is at least partially set or cured if not wholly so.

The various levels or zones in the apparatus are maintained by liquid-level controls and temperature sensitive controls to heating coils in treating zone. A cold wall or coil situated at the upper level of the vapor zone detennines the upper limit of the vapor zone. In the variation of equipment shown in FIG. 2 a condensing coil 12 offset and below the exit from the chamber condenses the vapors used in the intermediate zone 7 and establishes the upper level of the vapors in the zone. The condensate dropping from coils 12 falls into the heated sump from which it is withdrawn and transferred to storage for reuse in making up fresh treating solution which is that supplied to the treating zone.

Following similar procedure as before described and employing the equipment illustrated in FIG. 1 with but the exception that the treating of the fabric is conducted outside the machine, equally good results can be achieved. The treating agent is applied outside the machine in conventional manner such as by spraying doctoring or flooding the solvent-treating agent solution or dispersion onto the fabric 28 for example. The fabric 28 is passed into the housing 10 through inlet 11 in a manner to prevent the solvent carrier from evaporating from the fabric. The fabric passes over an idler roller 18. The roller 18 directs the fabric 28 into a vapor zone 29 wherein the fabric 28 passes over the heated rolls 19, 21, 22, 24 and 25 and over the idler rolls 20 and 23. The zone 25 is maintained full of solvent vapors by boiling the solvent from the sump 17. The fabric 28 passes out of the vapor zone 29 over directional rollers 26 and 27 which may be heated through quiescent zone 29b and out of the housing through outlet 12. It is to be understood that the rollers 26 and 27 while shown to be heated may not be heated under certain circumstances. The zone 29 is maintained full of vapors by boiling the solvent from sump EXAMPLE 1 A cloth of 9.1 oz. per square yard weight was passed through an apparatus of the same design shown in FIG. 1 at a rate of 22 inches per minute. The liquid in the bottom of the equipment was a commercial grade of stabilized 1,1,1- trichloroethane. The duration of the run was 275 minutes. The rollers were heated with steam to provide a surface temperature during passage of the cloth thereover of 250 F. At the end of the run the amount of solvent remaining in the equipment was measured. The bath was found to have lost 4.2 pounds of solvent which represents a loss (4.2/46.5) Ca 0.09 pounds per square yard.

In a blank run to determine whether any solvent was lost other than by carryout with the cloth, the equipment was operated for 945 minutes with the roll surface temperatures at 250 F. The solvent loss was 16.8 pounds. Assuming a straight line loss this represents a loss of about 1 pound per hour. This compares with a loss of 4.2 lbs/4.5 hours or 0.9 pounds per hour with cloth.

in another series of operations employing the same equipment but different times and cloth species the following results were obtained.

Employing an apparatus substantially as shown in H6. 1 a 17.6 ounce per square yard cotton cloth sprayed with a commercial grade of stabilized 1,1,l,-trichloroethane under 7.7 p.s.i. was introduced into the vapor zone and passed over the steamed heated rolls which were maintained at 250 F. by 30 p.s.i. steam. The vapor zone was maintained by passing steam through the coil in the bottom of the apparatus which was covered with a commercial grade of stabilized 1,1,1 trichloroethane. The cloth was passed through the zone for 11.75 minutes and measurements taken of the various feed tanks and reservoirs to determine their gain or loss. The various tanks showed that all but 1.32 gallons of solvent was recovered. This represented 91.2 percent recovery of solvent sprayed and employed in the process. The cloth was dry and had no characteristic odor of the solvent after leaving the ap paratus. The solvent loss was about 8.8 percent (0.0484 pounds) or about 0.0044 gallons per yard. Present day commercial operations report 15 to 25 percent solvent losses.

Thus there is established the fact that the halogenated solvent (which is volatile carrier for the treating agent) will im- I pregnate a cloth and can be recovered therefrom successfully and in economical amounts by employing the methods and apparatus here described.

EXAMPLE 3 In a representative operation employing an apparatus similar to FIG. 1 a solution of a commercial fluorine containing starch and water repellent in a commercial grade of stabilized l,1,1,-trichloroethane was sprayed onto a 22 ounce cotton fabric under 30 pounds er square inch pressure from 15 nozzles having openings of .026 inches. The fabric was immediately introduced into the machine. The concentration of repellent in the solvent was 0.625 percent by weight. The total weight of solvent sprayed was 86.5 pounds. The fabric was parged through the machine at a rate of about 12 yards per minute. The steam pressure in the steam heated rolls was 28 pounds p.s.i.

As a result of these operations there was obtained a cloth treated with the stain repellent which meet the repellent manufacturers produce speicifications.

The total solvent loss for this operation was 1.04 percent based on the total solvent employed in the spray solution and the boiling sump.

I claim:

1. Coating apparatus for treating a continuous length material comprising:

1. a generally closed housing having inlet and outlet means to accommodate said material and disposed respectively in opposite sidewalls thereof;

2. said outlet being elevated with respect to said inlet;

3. the bottom of said housing being compartmented to define at least two open-faced tanks disposed in parallel with said sidewalls;

4. the tank nearest the inlet containing coating stuff includ ing solvent and the tank nearest the outlet comprising a coiling tank and containing solvent and associated with heater means to boil said solvent whereby to effect an environment of solvent vapor above said tanks;

5. a continuous trough, horizontally disposed on the inner wall surfaces of said housing, substantially above said tank means but below said entrance and exit means and combined with a continuous cooling element therein;

6. a cooling channel means coextensive with said continuous trough means but disposed on the outer surfaces of said housing;

7. means communicating said trough with the boiling tank;

8. whereby is substantially defined the height of said vaporous environment, the defined cooling means effecting condensation of solvent vapor on the housing walls above said trough and the solvent recovered in said trough being returned to the boiling tank through said communicating means;

7 9. driven guide roll means disposed to define a path for said material from said inlet means, through said coating stuff by immersion, and through said solvent-vapor environment to said outlet;

10. infrared heating means located within the housing and disposed to treat the coated material;

1 1. second outlet means disposed at an uppermost portion of said housing for removal of residual atmosphere therefrom and associated with separator means for recovery of residual solvent from said atmosphere; and

12. means heating and delivering the balance of said removed atmosphere to said housing through the material outlet thereof whereby to further treat said coated material and to seal said housing with respect to the vapors therein. 

2. said outlet being elevated with respect to said inlet;
 3. the bottom of said housing being compartmented to define at least two open-faced tanks disposed in parallel with said sidewalls;
 4. the tank nearest the inlet containing coating stuff including solvent and the tank nearest the outlet comprising a coiling tank and containing solvent and associated with heater means to boil said solvent whereby to effect an environment of solvent vapor above said tanks;
 5. a continuous trough, horizontally disposed on the inner wall surfaces of said housing, substantially above said tank means but below said entrance and exit means and combined with a continuous cooling element therein;
 6. a cooling channel means coextensive with said continuous trough means but disposed on the outer surfaces of said housing;
 7. means communicating said trough with the boiling tank;
 8. whereby is substantially defined the height of said vaporous environment, the defined cooling means effecting condensation of solvent vapor on the housing walls above said trough and the solvent recovered in said trough being returned to the boiling tank through said communicating means;
 9. driven guide roll means disposed to define a path for said material from said inlet means, through said coating stuff by immersion, and through said solvent-vapor environment to said outlet;
 10. infrared heating means located within the housing and disposed to treat the coated material;
 11. second outlet means disposed at an uppermost portion of said housing for removal of residual atmosphere therefrom and associated with separator means for recovery of residual solvent from said atmosphere; and
 12. means heating and delivering the balance of said removed atmosphere to said housing through the material outlet thereof whereby to further treat said coated material and to seal said housing with respect to the vapors therein. 